The instant invention relates to a new use of radical-terminated co-oligomers (hereafter called "co-oligomers"). These co-oligomers are composed of a backbone terminated by a perfluoroalkyl moiety from 8 to 1000 carbon atoms, wherein the backbone of the co-oligomer is made up of non-ionic hydrophilic monomer units and anionic hydrophilic monomer units. The instant invention describes the incorporation of these co-oligomers thereof into compositions for fire-fighting foams used on polar solvent fires. Similar co-oligomers have been disclosed for fire-fighting compositions in U.S. Pat. 4,460,480. However, these compositions are limited for use with protein and only for non-polar hydrocarbon fires.
Certain perfluorinated compounds have been used in fire-fighting foam compositions because of their well-known extreme surface activity in aqueous medium (now surface tension at very low concengtration) and oleophoibicity (hydrocarbon fuel repellency).
U.S. Pat. Nos. 3,475,333; 4,472,286; 4,460,480 and 4,717,744; French Pat. Nos. 2,007,254 and 2,010,842; and European Pat. No. 19,584 teach that non-ionic perfluoroalkyl surfactants are especially useful for fire-fighting compositions such as aqueous film forming foam concentrates (AFFF) and/or protein-based foam concentrates. These compounds are shown to improve the effectiveness of the fire-fighting foam concentrates by the improved foam quality, and reduced foam flammability.
The use of perfluoroalkyl oligomers and polymers is specifically taught in U.S. Pat. Nos. 3,475,333; 4,472,286; 4,460,480 and 4,717,744. A fire-extinguishing composition which includes them can form a thin aqueous film on the surface of a flammable liquid and inhibit the reignition of the flammable liquid once extinguished. Further, for instance, the said fire-fighting composition can enhance the physical properties such as heat resistance of the foam resulting therefrom. The perfluorinated surfactants in the aforementioned patents are also incorporated into protein-based fire-fighting compositions in order to impart improved properties such as increased foam mobility, reduced extinguishing times, and reduced fuel pick-up. U.S. Pat. No. 4,460,480 teaches co-oligomers, a process for their preparation and their use as a component in protein foam fire-fighting compositions for fighting fires of burning hydrophobic or non-polar hydrocarbon liquids.
These prior-art compositions suffer from the fact that they are useful only on hydrocarbon fires, and are ineffective on polar solvents or hydrophobic solvents which contain a small proportion of polar solvent, such as gasohol. These latter type solvents, especially those miscible with water, have proven difficult to extinguish because they are not effectively sealed by the foam that contains only the perfluoroalkyl surfactants previously disclosed.
U.S. Pat. Nos. 3,957,657; 4,420,434; 4,424,133; 4,387,032; 4,306,979; 4,060,489; 4,464,267 and 4,060,132 describe the use of thixotropic polysaccharide gums in fire-fighting compositions for polar solvent fires. Unlike other types of fire-fighting foams such as AFFF, such foams are not destroyed by the solvent, and are suitable to fight fires on polar solvents as well as on hydrocarbon solvents and fuels and on solids that are compatible with the foam. Fire-fighting foams containing polysaccharide gums form a membrane on the surface of the polar solvent that protects the rest of the foam from collapsing. The thixotropic character enables the ready pumping of the foam and of the solution from which it is foamed.
Protein hydrolysates can be used in combination with polysaccharide gums to fight polar-solvent fires. The use of non-oligomeric ampholytic sulphonamide fluorochemical with hydrolyzed protein and polysaccharide gums to fight polar solvent fires has been described in U.S. Pat. No. 4,424,133. In this invention, an anionic polysaccharide gum is added to a film-forming fluoroprotein to stabilize the foam in this composition.
U.S. Pat. Nos. 4,303,534 and 4,563,287 describe an aqueous fire-fighting composition based on a perfluoroalkyl, high molecular weight polymer (greater than 5,000 AMU, and preferably greater than 10,000 AMU) which contains perfluoroalkyl groups interspersed along the polymeric backbone. These polymers were found useful as additives in fire-fighting foams for polar solvents as well as on cooking oil fires. They suffer from the fact that the perfluoroalkyl groups are not as efficient when distributed randomly along the polymer backbone as in the present invention where the perfluoroalkyl groups terminate the said co-oligomers.
U.S. Pat. No. 4,859,349 discloses complexes of anionic polysaccharides with perfluoroalkyl cationic surfactants which are useful in aqueous fire fighting compositions for fighting polar solvent fires. The instant invention differs from this reference by teaching the use of anionic polysaccharides and anionic perfluoroalkyl co-oligomers for fighting fires on polar liquids. No co-oligomers are disclosed in U.S. Pat. No. 4,859,349.
The instant co-oligomers, by virtue of their structure, are capable of concentrating on the surface of water or at the interface between water and hydrocarbon fuel forming an oriented surface layer. The prior art polymers require high molecular weight to attain the efficiency which the co-oligomers of the present invention can attain at much lower atomic weight and fluorine levels. The dynamic foam stability in formulations prepared from the above type materials were found to be much weaker than those prepared from the co-oligomers of the present invention. The fire-fighting compositions prepared from these polymers did not incorporate polysaccharide gums into the compositions, and as a result were found to be much weaker in their ability to extinguish polar solvent fires than those compositions of the present invention.
It has now been surprisingly found that perfluoro-terminated co-oligomers made by reacting a perfluoroalkyl moiety with monomers of type M.sub.1 and type M.sub.2 are considerably more useful and efficient in prolonging the foam stability of polar solvent foam concentrates when used in conjunction with polysaccharides as well as other polymeric materials.
Most importantly, it was found that co-oligomers when incorporated into concentrates greatly improve the efficiency of said concentrates and impart superior performance characteristics to polar solvent fire-fighting foams. These co-oligomers exhibit superior performance to perfluoro-terminated homo-oligomers of the non-ionic hydrophilic type or perfluoro-terminated homo-oligomers of the anionic hydrophilic type described in the prior art. In the prior art, these homo-oligomers were disclosed as additives to protein foam designed for use only on non-polar solvent fires.
The present co-oligomers are also more soluble in salt water than the homo-oligomers previously disclosed as well as being less soluble in polar solvents, such as isopropyl alcohol and acetone. This makes the co-oligomers of the present invention much more effective and of practical importance.
The co-oligomers have been found to be extremely efficient vapor mitigators, and prolong the lifetime of the foam, because the foam blanket which is formed is impervious to vapor penetration. As vapor suppressants they prevent the reignition of polar solvents. The co-oligomers interact with polysaccharides in a synergistic manner, and improve the performance characteristics required for efficient vapor mitigation. The synergism was found to be due to strong association of co-oligomers with the polysaccharides. The co-oligomers were also found to strongly interact with polymers of several other types, including natural and synthetic polymers when used in conjunction with polysaccharides. The natural polymers can be neutral or anionic polysaccharide or proteins or combinations thereof. Likewise, the synthetic polymers can be neutral or anionic.
Other polar solvent fire-fighting compositions which do not incorporate thixotropic gums have also been described in U.S. Pat. Nos. 4,303,534; 4,060,132; 4,306,979 and 4,536,298.
European Pat. No. 19,584 describes the preparation of products of the type: EQU C.sub.x F.sub.2x+1 --C.sub.2 H.sub.4 --S[CH.sub.2 CH(X)].sub.y H
where y can vary from four to 200 and X is particularly a --COOH or --CONH.sub.2 group, formed by free-radical oligomerization of a thiol C.sub.x F.sub.2x+1 --C.sub.2 H.sub.4 --SH with a vinyl monomer such as, for example, acrylic acid or acrylamide.
U.S. Pat. No. 4,460,480 describes preparation and use of co-oligomers of the type: EQU R.sub.f --E--S--[M.sub.1 ].sub.x --[M.sub.2 ].sub.y --H
and mixtures thereof wherein R.sub.f is a alkyl group, E is a linkage group, M.sub.1 represent a hydrophilic monomer unit, M.sub.2 represents a hydrophobic monomer unit, x and y represent the number of monomer units present in the co-oligomers. Both of these patents describe use of these co-oligomers for fighting non-polar hydrocarbon fires when used in aqueous film forming foam (AFFF) or fluoroprotein (FP). They were not described for use on polar solvent fires, nor for use in conjunction with polysaccharides.
Protein based fire-fighting compositions containing alkyl sulfide terminated oligomers are also described in U.S. Pat. No. 3,475,333 and British Pat. No. 1,245,124. These fluoroprotein foam compositions are also primarily designed for non-polar fuel fires and are not at all useful for fighting fires on polar solvents.